Uplink multi-user multiple-input and multiple-output (UL MU-MIMO) transmission request method in UL MU-MIMO communication

ABSTRACT

Provided is a method of transmitting and receiving a frame for a multi-user multiple-input and multiple-output (MU-MIMO) communication in an access point (AP), the method including transmitting, to each of a plurality of stations (STAs), an uplink multi-user request (UL MU request) frame requesting transmission of a data frame, and receiving, from each of the plurality of STAs, the data frame during an identical period of time based on an identical reception intensity, wherein the UL MU request frame includes at least one of information on a transmission time of the data frame and information on a reception intensity of the data frame in the AP.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/329,874 filed on Jul. 11, 2014, which claims the priority benefit ofKorean Patent Application No. 10-2013-0082771, filed on Jul. 15, 2013,Korean Patent Application No. 10-2013-0112573 filed on Sep. 23, 2013,and Korean Patent Application No. 10-2014-0013949 filed on Feb. 7, 2014in the Korean Intellectual Property Office, the disclosures of which areincorporated herein by reference.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention relate to a media access control(MAC) protocol of a wireless local area network (WLAN), and moreparticularly, to a configuration of a frame for use in frametransmission based on uplink multi-user multiple-input andmultiple-output (UL MU-MIMO) technology.

2. Description of the Related Art

Recently, in wireless communication systems, a multiple-input andmultiple-output (MIMO) technology for transmitting and receiving datausing at least two antennas is being generalized. A wireless local areanetwork (WLAN) also enables at least two transmission antennas to beused from the Institute of Electrical and Electronics Engineers (IEEE)802.11n standard. The IEEE 802.11n standard allows for use of up to fourantennas, and the IEEE 802.11ac standard allows for use of up to eightantennas. For example, in a case of using a great number of transmissionantennas, data transmission may be performed based on transmitbeamforming technology, thereby improving a performance of signalreception.

For efficient use of frequency resources, the IEEE 802.11ac for whichstandardization is in progress may include downlink multi-usermultiple-input and multiple-output (MU-MIMO) technology enabling anaccess point (AP) to simultaneously transmit beamformed data frames to aplurality of stations (STAs). Also, research is being conducted intouplink (UL) MU-MIMO technology enabling transmission of data frames tothe AP from the plurality of STAs and reception of the data frames atthe AP through being separated for each stream, to be conductedsimultaneously.

FIG. 1 is a diagram illustrating an example of a protocol used totransmit data based on UL MU-MIMO technology according to a related art.

Since stations (STAs) transmitting data based on the UL MU-MIMOcommunication are to simultaneously transmit beamformed data frames, anAP may need to perform a process of providing notification on a time atwhich a transmission is initiated. The process may correspond to a UL MUrequest sequence of FIG. 1. When the process ends, the STAs may transmitthe beamformed data frames after a predetermined period of time elapses.When the beamformed data frames are received from the STAs, the AP maytransmit, to each of the STAs, an acknowledgement (ACK) frame or a blockACK (BA) frame which corresponds to an ACK sequence of FIG. 1. Dependingon a necessity, a protection sequence for preventing channel accesses ofother STAs included in a basic service set (BSS) may be performed beforethe UL MU request sequence.

To successfully receive the beamformed data frames simultaneouslytransmitted from the STAs to the AP, a temporal length, for example, atransmission time of the beamformed data frame transmitted by each ofthe STAs may need to be the same, an intensity of a received signal mayneed to be almost the same, and a number of spatial streams (Nss) usedfor a transmission of each of the STAs may need to be acknowledged.

SUMMARY

According to an aspect of the present invention, there is provided amethod of transmitting and receiving a frame for a multi-usermultiple-input and multiple-output (MU-MIMO) communication in an accesspoint (AP), the method including transmitting, to each of a plurality ofstations (STAs), an uplink multi-user request (UL MU request) framerequesting transmission of a data frame, and receiving, from each of theplurality of STAs, the data frame during an identical period of timebased on an identical reception intensity, wherein the UL MU requestframe includes at least one of information on a transmission time of thedata frame and information on a reception intensity of the data frame inthe AP.

The UL MU request frame may include identification information on eachof the plurality of STAs, and the identification information may includeat least one of media access control (MAC) address information,association identification (AID) information, and partial AIDinformation in the Institute of Electrical and Electronics Engineers(IEEE) 802.11ac.

The UL MU request frame may further include information on a number oftransmission STAs.

According to another aspect of the present invention, there is alsoprovided a method of transmitting and receiving a frame for an MU-MIMOcommunication in an STA, the method including receiving, from an AP, aUL MU request frame requesting transmission of a data frame, determininga transmission time of the data frame based on the UL MU request frame,and transmitting, to the AP, the data frame during the determinedtransmission time, wherein the UL MU request frame includes thetransmission time of the data frame.

The UL MU request frame may include identification information on theSTA, and the identification information may include at least one of MACaddress information, AID information, and partial AID information in theIEEE 802.11ac.

According to still another aspect of the present invention, there isalso provided a method of transmitting and receiving a frame for anMU-MIMO communication in an STA, the method including receiving, from anAP, a UL MU request frame requesting transmission of a data frame,determining a transmission intensity of the data frame based on the ULMU request frame, and transmitting, to the AP, the data frame based onthe determined transmission intensity, wherein the UL MU request frameincludes information on a reception intensity of the data frame in theAP.

The determining may include determining the transmission intensity ofthe data frame based on the information on the reception intensity ofthe data frame in the AP.

The UL MU request frame may further include information on atransmission intensity of the UL MU request frame in the AP.

The method may further include determining a reception intensity of theUL MU request frame in the STA.

The determining of the transmission intensity of the data frame mayinclude calculating a path loss based on information on the transmissionintensity of the UL MU request frame in the AP and the receptionintensity of the UL MU request frame in the STA.

The determining of the transmission intensity of the data frame mayinclude determining the transmission intensity of the data frame basedon information on the reception intensity of the data frame in the APand the path loss.

According to yet another aspect of the present invention, there is alsoprovided an STA for use in an MU-MIMO communication, the STA including acommunicator to receive, from an AP, a UL MU request frame requestingtransmission of a data frame, and a controller to determine atransmission time of the data frame based on the UL MU request frame,and control the communicator to transmit the data frame to the AP duringthe determined transmission time, wherein the UL MU request frameincludes the transmission time of the data frame.

The UL MU request frame may include identification information on theSTA.

According to further another aspect of the present invention, there isalso provided an STA for use in an MU-MIMO communication, the STAincluding a communicator to receive, from an AP, a UL MU request framerequesting transmission of a data frame, and a controller to determine atransmission intensity of the data frame based on the UL MU requestframe, and control the communicator to transmit the data frame to the APbased on the determined transmission intensity, wherein the UL MUrequest frame includes information on a reception intensity of the dataframe in the AP.

The controller may determine the transmission intensity of the dataframe based on the information on the reception intensity of the dataframe in the AP.

The UL MU request frame may further include information on atransmission intensity of the UL MU request frame in the AP.

The controller may determine a reception intensity of the UL MU requestframe in the STA, and calculate a path loss based on information on thetransmission intensity of the UL MU request frame in the AP and thereception intensity of the UL MU request frame in the STA.

The controller may determine the transmission intensity of the dataframe based on information on the reception intensity of the data framein the AP and the path loss.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects, features, and advantages of the inventionwill become apparent and more readily appreciated from the followingdescription of exemplary embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is a diagram illustrating an example of a protocol used totransmit data based on uplink multi-user multiple-input andmultiple-output (UL MU-MIMO) technology according to a related art;

FIG. 2 is a block diagram illustrating an access point (AP) and stations(STAs) according to an example embodiment;

FIG. 3 is a timing diagram illustrating operations of an AP and an STAaccording to an example embodiment;

FIG. 4 is a flowchart illustrating a method of transmitting andreceiving a frame in an AP according to an example embodiment;

FIG. 5A is a diagram illustrating a configuration of a UL MU requestframe according to an example embodiment;

FIG. 5B is a diagram illustrating a configuration of a very highthroughput (VHT) presentation protocol data unit (PPDU) according to anexample embodiment;

FIG. 5C is a diagram illustrating a configuration of a UL MU requestframe including a VHT-signal (SIG)-A for use in a UL MU-MIMOtransmission according to an example embodiment;

FIG. 6 is a flowchart illustrating an example of a frame transmissionand reception method performed in an STA side according to an exampleembodiment; and

FIG. 7 is a flowchart illustrating another example of a frametransmission and reception method performed in an STA side according toan example embodiment.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments will be described in detail withreference to the accompanying drawings. However, it should be understoodthat these embodiments are not construed as limited thereto. Likereference numerals in the drawings denote like elements.

The terms used in this specification were selected to include current,widely-used, general terms, in consideration of the functions of thepresent invention. However, the terms may represent different meaningsaccording to the intentions of the skilled person in the art oraccording to customary usage, the appearance of new technology, etc.

In certain cases, a term may be one that was arbitrarily established bythe applicant. In such cases, the meaning of the term will be defined inthe relevant portion of the detailed description. As such, the termsused in the specification are not to be defined simply by the name ofthe terms but are to be defined based on the meanings of the terms aswell as the overall description of the present invention.

FIG. 2 is a block diagram illustrating an access point (AP) and stations(STAs) according to an example embodiment.

Referring to FIG. 2, an AP 100 may include a controller 110 and acommunicator 120.

The controller 110 may generate a frame transmitted by the communicator120. The controller 110 may process a frame received by the communicator120. The controller 110 may control the communicator 120 to communicatewith at least one of communicators 220-1 through 220-n of STAs 200-1through 200-n based on a multiple-input and multiple-output (MIMO)scheme.

The controllers 210-1 through 210-n may process frames received by thecommunicators 220-1 to 220-n, or generate frames transmitted by thecommunicators 220-1 through 220-n. The controllers 210-1 through 210-nmay determine one of a transmission time and a transmission intensity ofa data frame based on, for example, an uplink multi-user request (UL MUrequest) frame. The controllers 210-1 through 210-n may control thecommunicators 220-1 through 220-n to transmit the data frame based on atleast one of the determined transmission time and transmissionintensity. In the present disclosure, the transmission time may refer toa period of time during which transmission is performed.

The controller 110 or each of the controllers 210-1 through 210-n may beimplemented by, for example, an integrated circuit (IC) chip, amicroprocessor, a minicomputer, and the like. The controller 110 or eachof the controllers 210-1 through 210-n may determine, for example, anSTA communicating with the communicator 120. The controller 110 or eachof the controllers 210-1 through 210-n will be further explained withreference to the following descriptions.

The communicator 120 of the AP 100 may communicate with at least one ofthe communicators 220-1 through 220-n of the STAs 200-1 through 200-n.The communicator 120 of the AP 100 may transmit or receive the UL MUrequest frame and the data frame to or from at least one of thecommunicators 220-1 through 220-n of the STAs 200-1 through 200-n. Thecommunicator 120 may include a communication module such as an antenna,a modulator/demodulator, a frequency processing device, a filteringdevice, and the like.

FIG. 3 is a timing diagram illustrating operations of an AP and an STAaccording to an example embodiment.

In operation 310, the AP 100 may transmit a UL MU request frame to anSTA 200. The UL MU request frame may be a frame identifying atransmission STA and a frame instructing the transmission STA totransmit the data frame. The transmission STA may be preset to transmitthe data frame after a predetermined period of time, for example, ashort interframe space (SIFS), elapses in response to receiving the ULMU request frame. As another example, the AP 100 may perform a requestto send/clear to send (RTS/CTS) exchange before transmitting the UL MUrequest frame. In an embodiment, the UL MU request frame may include atleast one of information on a reception intensity and information on atransmission time of the data frame. For example, the UL MU requestframe may include at least one of a reception intensity applied when thedata frame is received in the AP 100 and a transmission intensity of theUL MU request frame of the AP 100.

In operation 320, the STA 200 may determine at least one of thetransmission intensity and the transmission time of the data frame basedon the UL MU request frame.

In operation 330, the STA 200 may transmit the data frame based on atleast one of the determined transmission time and transmissionintensity.

FIG. 4 is a flowchart illustrating a method of transmitting andreceiving a frame in an AP according to an example embodiment.

In operation 410, an AP may determine a transmission time for each ofthe plurality of STAs.

In operation 420, the AP may determine a reception intensity of the APin a case in which each of the plurality of STAs transmits the dataframe.

In operation 430, the AP may transmit, to an STA, the UL MU requestframe including at least one of the determined transmission time andreception intensity. For example, a configuration of the UL MU requestframe according to an example embodiment may be indicated with referenceto FIG. 5A.

Referring to FIG. 5A, the UL MU request frame may include a framecontrol field, a receiver address (RA) field, a transmitter address (TA)field, a UL MU-MIMO common information (UL MU-MIMO info) field,transmission STA information (STA info) fields, and a frame checksequence (FCS) field. The UL MU request frame may include thetransmission STA fields, and include identification information ontransmission STAs corresponding to STA1 through STAn. In an embodiment,the identification information on each of the transmission STAs mayinclude at least one of media access control (MAC) address information,association identification (AID) information, and partial AIDinformation in the Institute of Electrical and Electronics Engineers(IEEE) 802.11ac.

The UL MU-MIMO info field may include an L-LENGTH indicating atransmission time information field of the data frame, a Tx power levelindicating an AP transmission intensity information field, a RequestedTx power level indicating a requested reception intensity informationfield, and a # of STAs indicating a field of information on a number ofSTAs.

The L-LENGTH may be used for a LENGTH value included in an L-SIG of abeamformed data frame to be transmitted by each of the STAs during a ULMU-MIMO transmission interval.

When a presentation protocol data unit (PPDU) type of the beamformeddata frame is a high throughput (HT) PPDU or a very high throughput(VHT) PPDU, a LENGTH field of the L-SIG may be changed to a temporallength of a frame. Thus, when each of the STAs transmits the data frame,data of which an amount corresponds to the temporal length indicated inthe L-LENGTH may be transmitted.

The Tx power level may include information on a transmission intensityapplied when the AP transmits a UL MU request frame. The Requested Txpower level may include information on a reception intensity requestedwhen the AP receives a data frame.

The # of STAs may indicate the number of STAs to transmit data framesduring the UL MU-MIMO transmission interval. The UL MU request frame mayinclude STA info fields corresponding to the number indicated in the #of STAs.

In operation 440, the AP may receive the data frame. Each of theplurality of STAs may transmit the data frame to the AP during anidentical period of time. The data frame transmitted by each of theplurality of STAs may be received by the AP based on an identicalreception intensity. Here, “being identical” may be used to indicate anidenticalness in terms of a time or an intensity, or being providedwithin a predetermined error range.

Among all preambles of physical (PHY) layers configuring PPDUstransmitted by the STAs based on UL MU-MIMO technology, each preamblecorresponding to a portion of all preambles may need to be mutuallyequivalent so as to be received by the AP. A configuration of the VHTPPDU may be indicated with reference to FIG. 5B. In the configuration,each of a frame information field, for example, L-SIG, VHT-signal(SIG)-A, and VHT-SIG-B may include PHY layer control information.VHT-SIG-B may include different information for each spatial stream, andL-SIG and VHT-SIG-A may include identical information for each spatialstream.

L-SIG may include L-LENGTH and L-DATARATE. L-DATARATE of VHT-PPDU may befixed to be 6 mega bits per second (Mbps). Thus, a plurality of equalL-SIGs, each being identical to another may be generated based onL-LENGTH information with reference to FIG. 5A. A plurality ofVHT-SIG-As, each being identical to another may be generated byincorporating VHT-SIG-A used for UL MU-MIMO transmission in the UL MUrequest frame, and a related configuration may be indicated withreference to FIG. 5C.

FIG. 6 is a flowchart illustrating an example of a frame transmissionand reception method performed in an STA side according to an exampleembodiment.

In operation 610, the STA may receive a UL MU request frame from an AP.The UL MU request frame may include a transmission time of a data frame.

In operation 620, the STA may determine the transmission time of thedata frame based on the UL MU request frame.

In operation 630, the STA may transmit the data frame to the AP duringthe determined transmission time. Also, each of a plurality of STAs maytransmit the data frame during an identical period of time. In responseto the transmitting, the AP may receive the data frame from each of theplurality of STAs during an identical period of time, thereby stablyperforming a beamformed data frame transmission and reception.

FIG. 7 is a flowchart illustrating another example of a frametransmission and reception method performed in an STA side according toan example embodiment.

In operation 710, the STA may receive a UL MU request frame from an AP.The UL MU request frame may include information on a reception intensityof a data frame. For example, the UL MU request frame may includeinformation on the reception intensity of the data frame in an AP side,and a transmission intensity of the UL MU request frame in the AP.

In operation 720, the STA may verify the transmission intensity of theUL MU request frame in the AP based on the UL MU request frame.

In operation 730, the STA may verify an actual reception intensity ofthe UL MU request frame.

In operation 740, the STA may calculate a path loss based on the actualreception intensity of the UL MU request frame and the transmissionintensity of UL MU request frame in the AP.

In operation 750, the STA may determine a transmission intensity of thedata frame based on the calculated path loss. For example, the STA maydetermine the transmission intensity of the data frame in the STA inconsideration of the path loss and the reception intensity of the dataframe in the AP.

In operation 760, the STA may transmit the data frame to the AP based onthe determined transmission intensity.

The units described herein may be implemented using hardware componentsand software components. For example, the hardware components mayinclude microphones, amplifiers, band-pass filters, audio to digitalconvertors, and processing devices. A processing device may beimplemented using one or more general-purpose or special purposecomputers, such as, for example, a processor, a controller and anarithmetic logic unit, a digital signal processor, a microcomputer, afield programmable array, a programmable logic unit, a microprocessor orany other device capable of responding to and executing instructions ina defined manner. The processing device may run an operating system (OS)and one or more software applications that run on the OS. The processingdevice also may access, store, manipulate, process, and create data inresponse to execution of the software. For purpose of simplicity, thedescription of a processing device is used as singular; however, oneskilled in the art will appreciated that a processing device may includemultiple processing elements and multiple types of processing elements.For example, a processing device may include multiple processors or aprocessor and a controller. In addition, different processingconfigurations are possible, such a parallel processors.

The software may include a computer program, a piece of code, aninstruction, or some combination thereof, for independently orcollectively instructing or configuring the processing device to operateas desired. Software and data may be embodied permanently or temporarilyin any type of machine, component, physical or virtual equipment,computer storage medium or device, or in a propagated signal wavecapable of providing instructions or data to or being interpreted by theprocessing device. The software also may be distributed over networkcoupled computer systems so that the software is stored and executed ina distributed fashion. In particular, the software and data may bestored by one or more computer readable recording mediums.

The methods according to the above-described embodiments may berecorded, stored, or fixed in one or more non-transitorycomputer-readable media that includes program instructions to beimplemented by a computer to cause a processor to execute or perform theprogram instructions. The media may also include, alone or incombination with the program instructions, data files, data structures,and the like. The program instructions recorded on the media may bethose specially designed and constructed, or they may be of the kindwell-known and available to those having skill in the computer softwarearts. Examples of non-transitory computer-readable media includemagnetic media such as hard disks, floppy disks, and magnetic tape;optical media such as CD ROM discs and DVDs; magneto-optical media suchas optical discs; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory (ROM),random access memory (RAM), flash memory, and the like. Examples ofprogram instructions include both machine code, such as produced by acompiler, and files containing higher level code that may be executed bythe computer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations and methods described above, or vice versa.

Although a few embodiments of the present invention have been shown anddescribed, the present invention is not limited to the describedembodiments. Instead, it would be appreciated by those skilled in theart that changes may be made to these embodiments without departing fromthe principles and spirit of the invention, the scope of which isdefined by the claims and their equivalents.

What is claimed is:
 1. A method of transmitting and receiving a framefor a multi-user multiple-input and multiple-output (MU-MIMO)communication in an access point (AP), the method comprising:transmitting, to each of a plurality of stations (STAs), an uplinkmulti-user request (UL MU request) frame requesting transmission of adata frame; and receiving, from each of the plurality of STAs, the dataframe during an identical period of time based on an identical receptionintensity, wherein the UL MU request frame comprises a Tx power fieldand a Requested Rx power field, wherein the Tx power field includesinformation on a transmission intensity applied when the AP transmitsthe UL MU request frame, and wherein the Requested Rx power fieldincludes information on a reception intensity requested when the APreceives the data frame.
 2. The method of claim 1, wherein the UL MUrequest frame comprises identification information on each of theplurality of STAs.
 3. The method of claim 2, wherein the identificationinformation comprises at least one of media access control (MAC) addressinformation, association identification (AID) information, and partialAID information in the Institute of Electrical and Electronics Engineers(IEEE) 802.11ac.
 4. The method of claim 1, wherein the UL MU requestframe further comprises information on a number of transmission STAs. 5.A method of transmitting and receiving a frame for a multi-usermultiple-input and multiple-output (MU-MIMO) communication in a station(STA), the method comprising: receiving, from an access point (AP), anuplink multi-user request (UL MU request) frame requesting transmissionof a data frame; determining a transmission time of the data frame basedon the UL MU request frame; and transmitting, to the AP, the data frameduring the determined transmission time, wherein the UL MU request framecomprises a Tx power field and a Requested Rx power field, wherein theTx power field includes information on a transmission intensity appliedwhen the AP transmits the UL MU request frame, and wherein the RequestedRx power field includes information on a reception intensity requestedwhen the AP receives a data frame.
 6. The method of claim 5, wherein theUL MU request frame comprises identification information on the STA. 7.The method of claim 6, wherein the identification information comprisesat least one of media access control (MAC) address information,association identification (AID) information, and partial AIDinformation in the Institute of Electrical and Electronics Engineers(IEEE) 802.11ac.
 8. A method of transmitting and receiving a frame for amulti-user multiple-input and multiple-output (MU-MIMO) communication ina station (STA), the method comprising: receiving, from an access point(AP), an uplink multi-user request (UL MU request) frame requestingtransmission of a data frame; determining a transmission intensity ofthe data frame based on the UL MU request frame; and transmitting, tothe AP, the data frame based on the determined transmission intensity,wherein the UL MU request frame comprises a Tx power field and aRequested Rx power field, wherein the Tx power field includesinformation on a transmission intensity applied when the AP transmitsthe UL MU request frame, and wherein the Requested Rx power fieldincludes information on a reception intensity requested when the APreceives the data frame.
 9. The method of claim 8, wherein thedetermining comprises determining the transmission intensity of the dataframe based on the information on the reception intensity of the dataframe in the AP.
 10. The method of claim 9, wherein the UL MU requestframe further comprises information on a transmission intensity of theUL MU request frame in the AP.
 11. The method of claim 10, furthercomprising: determining a reception intensity of the UL MU request framein the STA.
 12. The method of claim 11, wherein the determining of thetransmission intensity of the data frame comprises calculating a pathloss based on information on the transmission intensity of the UL MUrequest frame in the AP and the reception intensity of the UL MU requestframe in the STA.
 13. The method of claim 12, wherein the determining ofthe transmission intensity of the data frame comprises determining thetransmission intensity of the data frame based on information on thereception intensity of the data frame in the AP and the path loss.
 14. Astation (STA) for use in a multi-user multiple-input and multiple-output(MU-MIMO) communication, the STA comprising: a communicator to receive,from an access point (AP), an uplink multi-user request (UL MU request)frame requesting transmission of a data frame; and a controller todetermine a transmission time of the data frame based on the UL MUrequest frame, and control the communicator to transmit the data frameto the AP during the determined transmission time, wherein the UL MUrequest frame comprises a Tx power field and a Requested Rx power field,wherein the Tx power field includes information on a transmissionintensity applied when the AP transmits the UL MU request frame, andwherein the Requested Rx power field includes information on a receptionintensity requested when the AP receives the data frame.
 15. The STA ofclaim 14, wherein the UL MU request frame comprises identificationinformation on the STA.
 16. A station (STA) for use in a multi-usermultiple-input and multiple-output (MU-MIMO) communication, the STAcomprising: a communicator to receive, from an access point (AP), anuplink multi-user request (UL MU request) frame requesting transmissionof a data frame; and a controller to determine a transmission intensityof the data frame based on the UL MU request frame, and control thecommunicator to transmit the data frame to the AP based on thedetermined transmission intensity, wherein the UL MU request framecomprises a Tx power field and a Requested Rx power field, wherein theTx power field includes information on a transmission intensity appliedwhen the AP transmits the UL MU request frame, and wherein the RequestedRx power field includes information on a reception intensity requestedwhen the AP receives the data frame.
 17. The STA of claim 16, whereinthe controller determines the transmission intensity of the data framebased on the information on the reception intensity of the data frame inthe AP.
 18. The STA of claim 17, wherein the UL MU request frame furthercomprises information on a transmission intensity of the UL MU requestframe in the AP.
 19. The STA of claim 18, wherein the controllerdetermines a reception intensity of the UL MU request frame in the STA,and calculates a path loss based on information on the transmissionintensity of the UL MU request frame in the AP and the receptionintensity of the UL MU request frame in the STA.
 20. The STA of claim19, wherein the controller determines the transmission intensity of thedata frame based on information on the reception intensity of the dataframe in the AP and the path loss.